Our house is a two-story built in 2011. We have zoned HVAC off a single unit with electronic dampers. The upstairs has three bedrooms and two bathrooms. The master bedroom is the only room that has a vaulted ceiling. The attic spans over all of the other upstairs rooms except for the master bedroom. The vents in all of the rooms are wide open and not blocked. The system's air filter is brand new. We have blackout curtains over the master bedroom window that are closed essentially all of the time.
When the upstairs thermostat (Nest 3rd Gen. in the hallway) calls for AC, the master bedroom cools off much slower than the rest of the rooms. We installed a Nest Temperature Sensor in the master bedroom so that the master bedroom stays the desired temperature, but this results in all of the other rooms being much colder than desired (typically 5-8 degrees colder than what the thermostat is set to).
Are there any solutions that we can deploy to balance the cooling in the master bedroom better with the rest of the rooms? Our HVAC guy just said it was because the master bedroom does not have the attic to assist with insulation, but I am not willing to accept that there is no solution.